Answer:
The correct answer will be-
1. Myelin sheath
2. Nodes of Ranvier
3. Speed up
Step-by-step explanation:
The neurons are the functional unit of the nervous system which acts to transmit the signals in the form of electrical impulses.
The axon of a neuron is covered by the layer composed of fats and glycoproteins which help to provide insulation to the neurons called myelin sheath. The myelin sheath also helps increase the transmission of the generated action potential through neurons.
The myelin sheath is not continuous at the axons but is reduced at certain points called nodes of Ranvier. These nodes of Ranvier contain the sodium voltage gates.
Thus, Myelin sheath, Nodes of Ranvier and Speed up are correct.